DIE SINKING, art of making tools, called dies, by means of which metals and other materials are pressed or cut into various shapes by a hammer or an ar rangement of levers. The die is usually cut from steel by a ma chine, but where extreme accuracy is required, e.g., when engraving dies for coins, goldsmiths' work and for some parts of machines, hand work predominates. Here an exact copy of the design is traced on a thin coating of wax spread over the prepared smooth surface, and is then engraved on the metal by recessing or sink ing. The tools used are chisels, gravers and rifflers, which are small files with curved ends for negotiating curves and recessed portions. First the sinker recesses the master die by engraving, in intaglio, the design on a piece of soft steel called the hub, which is then hardened to form the matrix. By means of the matrix, the design is expressed in relief on a second piece of softened steel called the punch which in turn is hardened and held in the press to strike the softened face of the working die. Several operations are necessary to bring the im pressions to a perfect state, the first blow being made on the die while in cone shape (see fig. ). The blow changes the form to that in the second view. The working die must then be an nealed, and its edge turned off a little smaller ; a complete, per fectly clean impression is pro duced, the die appearing as in the third view.
Considerable quantities of metal must be removed in sinking dies, and machine cutting, as far as possible, is essential to save hand labour. Dies which have the shape cut through from top to bottom, for press work, are roughed out on a metal jig-sawing machine, and finished on a slotting machine or a filing machine, which passes a file up and down while the die is held on a table and moved about as required. Large dies are often cut out by means of the oxy-acetylene blowpipe. A die-sinking machine, which is a milling machine, uses a variety of revolving cutters (see fig. 2). The difficulty with half-dies, pairs of which make cylindrical or spherical shapes, is the cutting of the half-round recesses. A cherry cutter is utilized for these ; instead of ing it is made to oscillate by the action of a curved slide on the machine, this motion (not required in other metal-working tions) cutting a half-round recess as sketched. The principle of the copying lathe applied to the die-sinking machine, enables it to cut any intricate shapes from a pattern in sheet metal, or sunk in iron or brass, the milling cutters being guided by the movement of an arm controlled by the pattern. Pantograph engraving and die-sinking machines also work from a copy, and cut the dies to an enlarged or reduced scale. A celluloid or sheet metal copy can be used also for guidance when cutting lettering, the copy being either in one piece, or made up of the separate letters or figures clamped in a holder.
